1. Field of the Invention
The present invention relates to a gas or liquid seal having compliant fingers riding on a shaft or other rotary body.
2. Description of the Related Art
Many classes of machinery utilize clearance seals to internally seal against a gas pressure. Often these seals are simple labyrinth seals which break down pressure by using a series of teeth or blades in close proximity to a rotating shaft. Devices such as these are well known and reliable, but allow high rates of gas leakage. Typically, clearances between the blade tips and the shaft are as high as 0.001 to 0.002 inches per inch of shaft diameter.
Much work has been done on reducing the leakage of labyrinth seals. This work has been directed toward improved blade geometry (e.g., backward angled blade designs), step seals, or interlocking blade designs to reduce losses. Particularly on jet engines, abradable seal designs are employed. The blades of such an abradable seal are initially installed with a line-to-line clearance, and then wear in to their own clearance as the machine rotates. However, after the rotor has gone through an operating history of radial vibration combined with axial excursions, the blade cuts a crescent shaped clearance into the abradable seal, and leakage can dramatically increase. Even with improved designs, leakage losses for labyrinth seals represent a considerable energy loss in rotating machinery.
Another significant problem with high pressure labyrinth seals is rotordynamic effects. Since high pressure gas is quite dense, a labyrinth seal begins to act as a bearing, except that it tends to destabilize the rotor since it is out of concentricity with the actual machine bearings. Significant work has been done recently to decrease rotordynamic excitation effects. This work includes swirl breaks in front of labyrinth, reverse swirl inducers, and injecting tangentially non-moving gas into the first stagnant region of the labyrinth. Other work is concentrated on optimized geometry and creating a rough surface within the labyrinth seal to retard circumferential gas velocity buildup. Also, honeycomb design labyrinth seals have been developed to reduce rotordynamic excitation effects. However, further reduction of rotordynamic effects is desirable.